Note: Descriptions are shown in the official language in which they were submitted.
2068931
WEB PICR-UP DEVICE
The present invention relates to a web pick-up device in the
press section of a machine for making fibrous webs of paper,
cardboard or the like. Web pick-up devices in the press section
S of a machine for making fibrous webs are Xnown in the art.
Running webs make contact in the press gap with a smooth
rotating surface from which the web runs off at the point of
pickup. The rotating surface and a suction box form together,
in the area of the pick-up point, a gap through which runs a
porous conveyor belt which receives the fibrous web.
Web pick-up devices of this general type are known, for
example, in the following publications:
1. U.S. Pat. 4,016,032
2. EP-A- 0364114,
3. EP-A- 0344088 (U.S. Pat 4,943,351)
4. EP-A- 0276202.
Similar devices are known from:
5. AT-PS 372,429
6. U.S. Pat 2,780,968.
On the devices known from publications 1 and 2, a suction
roll is arranged on a press roll which features a smooth roll
shell that makes direct contact with the fibrous web. A porous
conveyer belt, preferably a so-called dry wire, runs across this
suction roll. The press roll and the suction roll form together
a gap through which passes the conveyer belt. The ob~ective
with this arrangement is to have the porous conveyer belt (by
means of the suction prevailing on the suction roll) pick up the
fibrous web from the press roll and transfer it to the
subsequent drying section. This is achieved ~o that the pickup
of the web from t~e smooth press roll occurs in a way such that
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the web will constantly be supported by some means of transport,
namely first by the shell of the press roll and thereafter by
the conveyer belt.
This is to avoid the presence of a free web train between
the press shel} and the conveyer belt. As i8 generally known,
such a free web train causes an undesirable longitudinal stretch
in the fibrous web, which at this point ~s st$11 moist and
possesses only little tens~le strength. It must also be taken
into account here that the ~till moist fibrous web clings at a
relatively high adhesive force to the smooth shell of the press
roll. By selecting a suitable shell material (for instance
granite, artificial stone or plastic) it is attempted to reduce
the adhesive force. Nevertheless, the lon~itud~nal stretch of
the web at the point of pickup remains a problem. ~ue to this
longitudinal stretch, it happens relatively frequently during
the operation that the fibrous web breaks at the point of pickup
or in the subsequent drying section, thereby interrupting the
production.
It had been difficult to establish the use of the
aforementioned devices (where an attempt is made to avoid a free
web train) in practice because of other difficulties. One of
these difficulties consists in the following: As known, modern
paper machines are generally dimensioned for an extremely l~rge
web width (in the order of up to 10 m). Therefore, all of the
rollers must have a correspondingly larqe length, for which
reason they undergo, under their deadweight and the respective
load, a more or less heavy sagging. In the case of the known
web pick-up devices, the consequence of thls is that it i8
practically impossible to produce an exactly uniform gap between
the press roll and the suction roll, without forcing the suction
roll on the press roll. But such contact pressure must be
avoided because the web would otherwise be damaged by the porous
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conveyor belt. It must be taken into account here that the
porous conveyor belt (preferably a so-called dry wire, which
subsequently carries the web from the point of pickup through
part of the drying section) has a considerably coarser structure
than the wet felts used in the press section, and that the
conveyer belt (normally) ~ust be made endless by means of a
seam.
Further known web pick-up devices have been described in
publication 3. According to Fig. 17, the fibrous web to be
dewatered runs between a felt and a smooth surface of a press
belt through the press gap. Behind the press gap, the press
belt and the web run with the roll shell and the press roll up
to a point of pickup where a conveyer belt (for example a dry
wire) is tangent with the press roll shell and receives the web
from the press belt. Behind the point of departure, the
conveyer belt runs to~ether with the web along a straight
section to a roll situated in~ide the conveyer belt loop (guide
roll or drying cylinder).
In other embodiments of the publication 3, the press belt
runs together with the web from the press gap first across an
additional support roll, on the circumference of which the point
of pickup is provided; that ~g, the dry wire touche~ at the
point of pickup the support roll, picking the web up at that
point; in several embodiments again with the aid of a vacuum box
which, for example, may be fashioned as a suction box. All of
the devices known from publication 3 have the disadvantages that
the mentioned press belt means not only additional expenditure,
but may now and then also cause an interruption of the
operation, namely when it needs to be replaced by a new press
belt because of wear.
In the case of another known web pick-up device
~publication 4), the fibrous web to be dewatered runs directly
" 2068931
on the smooth surface of the press roll shell from the press gap
to the point of pickup, where it is received again by a conveyer
belt. For separating the web from the smooth surface of the
press roll there is an electrical induction hQater provided.
Interactinq with the magnetically conductive shell material of
the press roll, this heating device is supposed to effect a
noncontact heating of the roll shell, and specifically the
fibrous web, in order to thereby reduce the adhesive force of
the moist web on the press roll shell. However, such a device
involves a high consumption of energy. Besides, as compared to
a simple suction device, it would appear to be more difficult to
establish a reliable and troublefree continuous operation.
The problem underlying the invention is to provide a web
pick-up device, wherein during continuous operation the picXup
of the fibrous web from the smooth press roll and the advance of
the web to the following drying section can take place with
greater safety than heretofore, i.e., with a lessened risk of
web breaks. At the same time, ~ust as with the known
arrangement, a free web section is to be avoided, 80 that in the
region of the web pick-up device no longitudinal stretch of the
fibrous web will occur, or at the most a very slight
longitudinal stretch will occur.
It is an object of t.he present invention to provide a novel web pick-
up device which obviates or mitigates at least one of the above-mentioned
disadvantages of the prior art. A~cordingly, the present invention, ln one
form thereof, comprises a web pick-up devioe for the press section of a
machine for making fibrous webs of the type wherein a running
web makes contact in a press gap with a smooth rotating surface,
and wherein the web departs said surface at a point of pickup.
The rotating surface and a suction box form together a gap in
the area of the point of pickup, through which gap runs a porous
conveyer belt, which belt receives the fibrous web. The suction
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box ~ p$vo~ab1y mountod, and ha~ in the are~ o~ the po~nt of
plckup a ~l~ding sur~ace acro~ whloh lld~8 ~h~ conveyer belt.
~h~ dlng ~urf~ce ~ ~rr~ngo~ at an ad~u8table ~p~a$ng ~rom
t2~e smooth rotating ~ur~ace during o~ra~ior of t~e dovlc~
~paalng i- d~te~n~d by ~ 6top on which~ uo~ion box b~rs
during op~ra~$on under th~ ~r~ect o~ ~ f~oxible li~t devlce.
~he invent~on i~ b~ad on the in-lg~t t~at lt i~ import~nt
to have the porow ~onveyer belt, ln the¦ara~ of tl~ ~o$nt o~
pickup, ~uppor~d b~ a oliding ~urfac~ w~lich ~an b~ ad~u~ted to
a ~ery ~mall dist~noe fro~ the ~mooth ~u: r~a~ ~pre~s~ably th~
pre~ roll 1t~el ). 2rovldad on th~ ~uo tion ~ox, thi~ ~llding
~ur~c~ -- in whic~ pro~erably ~ 8uctlon op8nlng ~or ln~tance a
~uction olot~ 1~ arr~ngod -- ~hould. b~ ~I r~ng~d, e.g., at a
diotan¢e betw~n 3 and 10 mm rro~ the ~m~oth ou~o~. ~ho
o~t;l~81 ~p~olng n~o~- to b~ ~-torm~n-~ o~er~t~on~ or whicl~
r-a~on th~ ~uc~on box need- to be pi~o~able, oo ~h~t th~
dl-t~nce can ~ dQtermin~d by ~n ad~u~t~ top.
It ~B ~l~o import~nt t~t th~ ~uct~on box i~ op~r~t~on~ly
not ~cur-d rl~idly to t~ top, but that ~ forced only
g~ntly on thlo ~top under th~ t~o~t o~ x~blo lift d~ce.
Thus, t~e apacin~ bo~weon uct~on box ald th- ~moot~ ~ur~ac~
(~or ln~tanc~ th~ preBO ~oll) ~a~ during t~ op~r~t~on, 1
n40ded, b~ lncr~sd a~to~atlcally, for instanc- lt ~ibor
~tor~al lu~p~ ~60~a~10d ~lob~) or otht~ cont~m~natlon- proc~d
~5 ~n th~ oa~ o~ oper~ion~l troublo togeth~ w~th th- Sibrou- w-b
~c~oe~ ~o p~s~ roll. Thl~ ~old~ da~ig~ to the ~ooth
~ur~ao~ ~for lnstan~o o~ tho pre-c rolllh~ll) or to th~
conv-yer bQlt or th~ ing u~ac- o~,t~ uctlon ~ox durlng
such ~n occurr~no~. I
~o As with th~ known ~ovlce~, the w~b 16 cont~n~ou~ly ~n
contac~ w~h ~ome m~an~ ot tran~port; namely, ~t ~a~s aont~ot
with th~ conv~ye~ belt already b ~or- ~ lng plc~ up ~rom
` 2068931
press roll. Thus, a free web train is avoided. The running
speed of the conveyer belt and the peripheral speed of the press
roll will normally be adjusted to the same value by control of
the respective drive facilities. In this case, the longitudinal
stretch of the fibrous web at the point of pickup equals zero.
But with the inventional arrangement it is also pQssible to run
the conveyer belt slightly faster than the press roll. In this
case, then, a longitudinal stretch of the fibrous web takes
place intentionally, but it is considerably less pronounced than
in the presence of an open web train.
A particular advantage of the inventional web pick-up
device is constituted in that it enables with simple means a
separation of the web directly from the smooth press roll shell.
In other words: contrary to publication 3, an additional,
outwardly smooth press belt is dispensable. Depending on
circumstances, however, the presence of such a press belt may
for specific reasons be desirable, for instance in order to
obtain a relatively soft press gap. In this case, too, the
inventional web pick-up device i8 applicable.
Another advantage is that the inventional device can
nonproblematically interact with a conveyer belt which has been
made continuous by means of a seam.
The drawi~g shows schematically a web pick-up device at the
last press of a paper machine.
In the embodiment depicted by the drawing, a lower press
roll 10 and a backing roll 7 form a press gap 8 through which
passes the web to be dewatered, together with a felt 6. The web
makes contact with the smooth surface 11 of the press roll 10.
The latter, e.g., is a known stone roll made from natural
gran~e or a roll with a plastic coating. The ob~ective in both
~06893~
cases is to so fashion the ~mooth surface 11 of the press roll
I0 that the as yet moist fibrous web will cling to the roll
shell with as low an adhesive force as possible.
The direction of rotation of the press roll 10 is indicated
by arrow P. Thus, the fibrous web runs in the drawing from top
to bottom toward a point of pickup A. A scraper 12 is arranged
in the lower area of the press roll 10 in the usual way.
A porous conveyer belt 13 runs shortly before the point of
pickup A onto the press roll 10. The conveyer belt 13 is
supported by a horizontally movable guide roll 14 located above
the point of pickup A and, below the point the poin' of pickup
A, by a suction guide roll 1~. Thus, the conveyer belt 13 forms
together with the press roll 10 a small wrap angle w, the size
of which can be varied by shifting the guide roll 14
horizontally. The conveyer belt 13 receives the fibrous web at
the point of pickup A and passes it across the suction guide
roll 15 to at least one subsequent drying cylinder 16. Next,
the conveyer belt 13 (forming an endless loop~ returns to the
guide roll 14.
At the point of pickup A and within the endless loop of the
conveyer belt 13 there is a suction box arranged, which overall
is referenced 20. It has in its upper area a suction chamber 21
with at least one suction slot 22 situated as close as possible
to the point of pickup A. The suction slot is located in the
area of a predominantly flat sliding surface 23, across which
slides the conveyer belt 13.
Following the sliding surface 23 there is a guide surface
24 provided, which as well is predominantly flat and diverges
from the running direction of the conveyer belt 13 at a ~mall
angle. This part o~ the suction box 20 has thus the effect of a
so-called web stabilizer. In other words: a suction is
generated during the operation in the wedge-shaped space 25
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between the guide surface 24 and the conveyer belt 13, by the
running conveyer belt 13. The higher the operating speed of the
paper machine (which ranges between 500 and 2Q00 m/min), the
greater the vacuum. The guide surface 24 extends up into the
entrance gore 35 between the suction guide roll 15 and the belt
13.
Thus, between the point of pickup A and the suction guide
roll 15 there is constantly a vacuum exerted on the f~brous web,
whic~l suction acts through the conveyer belt 13, causing the
fibrous web to be sucked up to the conveyer belt. This section
of run being at least predominantly straight, no eccentric force
(at any rate no appreciable eccentric force) acts in this region
on the fibrous web.
The suction box 20 pivots about a bearing 26. The bearing
26 is arranged in the lower area of the suction box, so that in
the upper area a spacing may be adjusted between the sliding
surface 23 and the surface 11 of the press roll 10. For that
purpose, an adjustable stop 27 is provided on both ends of the
suction box 20, on which stop the suction box is forced by means
of a pneumatic, and thus flexible lift device 28. The lattQr i8
supported by a stationary component 28a with which the stop 27
(which may be fashioned as a screw) also makes contact.
Additionally, a tension spring 29 may be provided which
counteracts the lift device, reducing its contact force. Thus,
the suct~on box 20 can escape easily in the event that a
contamination approaches the point of pickup A along with the
fibrous web. In this context, the sliding surface 23 may be
provided, before the suction slot 22, with a (not illustrated)
rounding. The air boundary layer carried along by the conveyer
belt 13 is deflected upward (arrow L) by a scraper strip 9, made
for instance of felt material, which is arranged on the top side
of the suction box 20 (in the area of the wrap angle w).
2068931
Schematically illustrated, in addition, is a suction line
31 connected to the suction chamber 21, and a suction blower 30.
The latter can pass the suctioned air into the open (line 32)
or, via a pressure line 33, in a blowing chamber 34 attached to
the suction box. Thiæ blowing chamber 34 forms the already
mentioned guide surface 24 and, if required, a blowing 810t 37
to further boost the vacuum in the space 25. The blowing
direction of the slot 37 is opposite to the running direction of
the suction guide roll 15 and enhances the vacuum present in the
gore 35 by ejector effect.
Additionally, as known as such, channels 38 originating
from the guide surface 24 may be provided which extend crosswise
through the blowing chamber 34, whereby the vacuum prevailing in
the space 25 can be increased.
The air discharging from the blowing slot 37 is suctioned
off again by a presuction zone 36 of the suction guide roll 15.
In other words: a safe sucking of the web onto the conveyer
belt is provided for also at the point where the conveyer belt
13 approaches the suction guide roll 15.
In variation from the drawing, the suction slot 22 may al80
be omitted. In this case, the suction ef~ect of the suction box
is achieved solely through the interaction of the stripper bar 9
with the diverging guide surface 24.
While this invention has been described as having a
preferred design, the present invention can be further modified
within the spirit and scope of this disclosure. This
application is therefore intended to cover any variations, uses,
or adaptations of the invention using its general pr$nciples.
Further, this application is intended to cover such departures
from the present disclosure as come within known or customary
practice in the art to which this invention pertains and which
fall within the limits of the appended claims.
